The highest temperatures in turbofan engines are typically found in the combustor and the turbines. The continuing demand for larger and more efficient turbofan engines creates a requirement for increased turbine operating temperatures. However, as the combustor and turbine hot gas temperatures have been increased to achieve increased output and thermal efficiencies, the challenge to maintain control and accessory component lives, due to the metallurgical limitations of critical hot components has also increased.
Turbofan engines equipped with a valved core compartment cooling (CCC) system typically extract cooling air from the fan stream and includes a core compartment cooling valve and cooling manifold to provide cooling to the control and accessory components located undercowl. In the prior art, control of the core compartment cooling valve was achieved as a function of altitude and engine core speed. However, the major control parameter for a typical turbofan engine is corrected fan speed. Takeoff, MCT (maximum continuous), climb and cruise regimes are defined by a given range of corrected fan speed, and there is only a weak relationship between uncorrected core speed and takeoff, MCT, climb and cruise regimes. Consequently, controlling the CCC valve as a function of uncorrected core speed resulted in forcing the valve to be opened in cruise conditions where it could have been closed, resulting in some inefficiencies at cruise and loss of specific fuel consumption.
Furthermore, prior art CCC valve schedules do not take into account the ambient conditions resulting in forcing the valve to be opened in cruise conditions regardless of the outside ambient temperature. The schedule is defined to maintain an acceptable undercowl temperature environment at the worst case condition to meet Federal Airworthiness Requirements, which is an extreme hot ambient condition and causes the valve to be opened at cooler temperatures where it could be closed, again resulting in some inefficiencies at cruise and consequent loss of specific fuel consumption.
Furthermore, prior art CCC valve schedules do not take into account the heat loads introduced by the aircraft ECS (environmental control system) bleed air system. The schedule is defined to maintain an acceptable undercowl temperature environment at the worst case condition to meet Federal Airworthiness Requirements, which corresponds to the highest aircraft ECS demand and therefore the highest heat loads and causes the valve to be opened at normal ECS demand conditions where it could be closed, again resulting in some inefficiencies at cruise and consequent loss of specific fuel consumption.
It is an object of the present invention improve efficiency of core compartment cooling to valve scheduling.
It is a further object of the present invention to provide core compartment cooling valve scheduling as a function of corrected fan speed, altitude, ambient conditions and aircraft environmental control system bleed air demand.
It is yet another object of the present invention to be able to adjust the schedule very precisely to improve efficiency.